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From: mmvvmm@mixcom.COM (Daniel Offutt)
Newsgroups: sci.bio
Subject: biomass as a measure of "success"
Message-ID: <1053@mixcom.COM>
Date: 21 Jun 91 19:50:39 GMT
Organization: Milwaukee Information eXchange (Public access Usenet, Email)
Lines: 42

How is the evolutionary "success" of a species measured?   The population
size alone does not seem a reasonable measure, since typical members from
different species may tie up different quantities of resources.  The total
mass of elephants on earth may be greater, for example, than the total mass
of mice, even though there are many fewer elephants than mice.

"Biomass" has been proposed as a general method for measuring the relative
"success" of different species.   But upon closer inspection, the concept
of a species' total biomass has some problems.  Consider man.  Which masses
count as part of man's total biomass?  All human bodies should be counted,
of course.  But why wouldn't man's artifacts also be counted as part of
man's biomass?  Should robins' nests be counted as part of the biomass of
robins'?   Should the hives bees build be considered part of the biomass
of bees?  It seems to me that the answer has to be "yes."  It also seems
that that answer leads to yet other conceptual difficulties.

How does one know that a given mass, such as a robin's nest, should be
included in the robin's biomass?  If the robin uses twigs torn from
a living tree, then are the twigs (1) no longer part of the tree's
biomass, or (2) part of both the tree's and the robin's biomass?
Does it matter which organism has "control" of a given mass?  So that
when the tree "controls" the mass of the twig, the twig counts as
part of the biomass of the species of tree, while when the robin "controls"
the twig, the twig is part of the biomass of robins?  What exactly does
"control" mean in this context?  How would a case in which "control" is
shared between members of different species be handled?  

Consider an ant hive, or any other underground tunnel dug by an animal.
The tunnel itself has no mass.  Yet I feel compelled to say that a species
of animal that digs burrows is tying up, and has control of a greater
quantity of resources than an otherwise identical species (in size and
structure) that does not dig burrows.  If you want to count the earth
around the burrow as the additional biomass, then how much of it do you
count, and where do you draw the boundary?

Maybe the answers to these questions have something to do with the amount
of "order" created by the members of a species, or the amount of energy
expended by the members per units time, on average.

Comments and criticism are welcome.

Dan Offutt